1. Field of Invention
This invention relates to "run-flat" tubeless, pneumatic tires that require internal support to provide the run-flat capability.
There are two other relevant competitive categories of run-flat tires that include: (1) those that require no internal support, and depend on extra thick side walls for run-flat capability; and (2) those that require no rigid internal support and use separate inner and outer concentric air chambers so that the inner chamber will support the load when the outer chamber loses pressure.
2. Prior Art
After almost 100 years of pneumatic tire use, there has been no widespread commercial use of any type of run-flat tires. However, there have been some attempts. The Dunlop Tire Co. attempted to market a run-flat tire using internal support in the mid-1970's. It required a special multi-piece wheel, and the use of an automatic releasable lubricant. It did not succeed. Dunlop had to set up special facilities for tire repair throughout the United Kingdom. The extra time, inconvenience and cost for repair was probably a major factor in its failure (Rubber Age, page 70, Sep. 1973; Rubber World, page 44, Apr. 1976).
There is, however, a run-flat tire in production for the military. The U.S. Army uses a run-flat tire with internal support on most of its wheeled vehicles (Automotive Engineering, Aug. 1986, page 25). According to the Army Technical Manual, these vehicles, in run-flat operation are limited to 30 m.p.h. for 30 miles, and it takes 2.2 hours to repair the tire. The long repair time appears due to the fact that it requires a special multi-piece wheel that must be bolted together, and also requires the use of a container of releasable lubricant/coolant that must be cleaned out and replaced when the tire is repaired. The Army tolerates the repair difficulties by carrying a spare tire or by driving to the motor pool and dropping off the flat, and replacing it with another premounted, run-flat tire. This practice could not work for the civilian market.
There is a beginning of commercial activity in run-flat tires without internal support that use extra thick sidewalls for support. In the fall of 1992, Bridgestone was working on run-flat tires specifically for the Corvette. Goodyear is planning a run-flat tire for 1993. Both require the use of electronic sensors to detect low pressure.
Those extra thick sidewalls, which carry the weight in run-flat operation, also carry the penalty of greater rolling resistance in normal highway driving. If there is even a minor loss of tire pressure, rolling resistance and heat buildup escalate rapidly. That is why these tires come equipped with expensive electronic low pressure warning devices. This higher rolling resistance adversely affects tire life and gas mileage, and is not an insignificant drawback to this type of run-flat. This extra thick sidewall type of run-flat appears to be limited to relatively low aspect ratio tires that are generally used in high performance sports cars.
Run-flat tires with separate air chambers have been on and off the market since the 1930's. Presently, Goodyear makes this type of run-flat tire for professional race cars. The problem with this type of run-flat is that the cause of the flat, such as a nail puncture or other road hazard, may also puncture the internal reserve air chamber and therefore reduce its reliability.
Since my run-flat tire requires the use of internal support, my prior art patent search is mostly limited to that category (Class 152/520 and 152/158). I found over 100 patents in this sub-class issued over the last 45 years. The earliest patent I found on run-flat tires using internal support in pneumatic tires was in 1937 (U.S. Pat. No. 2,067,545). It had a metal annular internal support rim integrated with the inner tube. (This was before the use of tubeless tires). This internal support was a separate unit from either the tire or the wheel and it required the use of a special multi-piece wheel.
In general, run-flat tire patents with internal support differ from each other in the manner that they solve problems that are common to all such run-flat tires. Below I am listing five features of my invention that deal with the various problems of run-flat tires. For each of these five features I found between five and ten patents with at least one of these features. Several patents had two or three of these features. None of these patents had more than three of these features. Also, the features in these patents took a different form and served a different purpose than the same features in my invention.
For each of these features, I have listed one patent that most closely relates to my invention, along with appropriate comments. The features are as follows:
Feature #1
Run-flat tires with internal support that use a standard one piece drop center wheel, with all the run-flat capability built directly into the tire. Example: Patent #1,022,483; Federal Republic of Germany, Jan. 1958. This particular feature helps make tire changing quicker and easier, as compared with run-flat tires that have run-flat capability built into the wheel. Also, being able to use standard wheels make run-flat tire sales feasible for the replacement tire market. The structure of the internal support in all of the patents with this feature were totally different from the structure of the internal support of my invention.
Feature #2
The internal support unit, when in run-flat operation, is designed to push outward against the wheel-rim flanges, which in turn pushes outward against the tire bead flanges. Example: Patent #1,305,383, United Kingdom, Jan. 1973. This feature aids in keeping the tire on the wheel in run-flat operation. This particular feature contributes to the feasibility of using the conventional one piece, drop center wheel as in Feature #1. The structure of my internal support with this feature was totally different from all the other patents that I saw with this feature.
Feature #3
The internal support consists of a multiple number of separate segments instead of an annular internal rim. Example: Patent #2,309,814, Federal Republic of Germany, Sep. 1974. I could not figure out the purpose of the intermittent support for some of these patents. In the example above, the purpose appears to provide an easy way to insert the inserts in the tire after the tire has been mounted on the wheel. In my invention this feature is a critical component in the method I use to eliminate internal sliding friction in run-flat operation. The structure of these separate inserts was different from those in my invention. None appeared to be used to solve the internal friction problem, as does my invention.
Feature #4
The internal support has shock absorbing capability. Example: Patent #2,309.814, Fed. Rep. of Germany, Sep. 1974. This feature is found in many run-flat tires with internal support. It is often found as a by-product from other features as in the patent example in Feature #1, and the patent example in Feature #2. This feature was deliberately added in the patent example in Feature #3. In my invention, this feature was also a by-product of other features. This is an important feature because it makes run-flat driving more comfortable, and reduces the chance of damage to the tire, inserts, axles and suspension components, during run-flat operation.
Feature #5
The internal support unit eliminates sliding friction without the use of a lubricant/coolant.
Most of the prior art of all run-flat tires with internal support rely on the use of a releasable lubricant/coolant to reduce this internal support friction problem. In many of these patents, this problem is not referred to, nor is a solution suggested, but the problem clearly exists. The patent office has a separate sub-class on releasable lubricant concerning chemical composition, containers, and method of release of the lubricant.
Almost all of the prior art patents that do not require the use of an internal lubricant use some type of roller or ball bearing integrated in the internal support unit to eliminate sliding friction. Example: U.S. Pat. No. 4,901,779, Feb. 6, 1990. Those patents did not relate in any way to my method of eliminating sliding friction.
There was one patent that used a method of eliminating sliding friction that was similar in concept to my invention. This was: U.S. Pat. No. 3,682,218, Aug. 1972. This patent and this feature merit more detailed explanation than the previous four features. This patent is also the most important prior art relating to my invention.
This U.S. patent invention consists of a metal, annular internal support rim attached to a special multi-piece wheel. A thick rubber tread is bonded to the metal rim surface of this internal rim. There are wide transverse gaps cut into this annular rubber tread which create a number of separate elastic rubber blocks. Under run-flat loading, these elastic rubber blocks are deformed by a combination of shear-compression loading that increases the distance between adjacent rubber blocks under load. This results in an increase in distance between adjacent blocks under load which automatically adjust for the difference in rolling circumference of the internal rim support and the rolling circumference of the tire. This action prevents sliding friction between the internal support rim and the inside of the tire tread.
The detailed description of my invention should make it clear the similarities and the differences between my invention and this prior art.